Abstract Background: Evidence suggests coordination of hospital obstetric service across hospitals with graduated service levels, termed regionalization, could improve maternal and perinatal mortality and morbidity. However, research related to these outcomes with regionalization focuses on perinatal outcomes, is hindered by lack of linked data sets, and uses proxy measures of hospital service level. The purpose of this study is to investigate the association between hospital obstetric service level and maternal and neonatal mortality and morbidity as well as resource use for women with high risk of obstetric complications. Specific Aims: 1) Identify associations between delivery hospital level of obstetric service and maternal outcomes for women at high risk of obstetric complications. 2) Identify associations between delivery hospital level of obstetric service and neonatal outcomes for children of women at high risk of obstetrical complications. 3) Identify associations between delivery hospital level of obstetric service and length of stay for women at high risk of obstetrical complications. Significance: This study will provide estimates of the association between graduated levels of obstetric service and both obstetric and neonatal outcomes to inform policy decisions regarding implementation of regionalization of obstetric service. In addition, this study will provide evidence to support clinical decision making regarding transfer of obstetric care for high risk women. Innovation: This study evaluates hospital regionalization using hospital discharge data linked to vital statistics records from birth certificates as well as maternal, fetal, and neonatal death. This innovation allows this study to estimate associations between hospital obstetric service level and maternal, fetal, and neonatal mortality both in and out of the hospital, while controlling for obstetric risk factors and neonatal service level. Methodology: This is a retrospective analysis of the Georgia Maternal Child Health Repository Data Base for the years 2009 through 2013. The sample is restricted to women identified as high risk for obstetric complication as measured by a validated maternal comorbidity index. Hospital obstetric service level will be measured using the CDC LoCATe Tool which has been designed to coincide with the recently developed graduated levels of obstetric care. Hierarchical modeling will be used to estimate the odds ratio for maternal, fetal and neonatal mortality as well as maternal and neonatal morbidity at each obstetric service level using hospitals with the highest obstetric level as reference. In addition, the difference in median length of stay for high risk women at hospitals with each obstetric service level will be estimated.